1. Field of the Invention
The present invention relates to an oscillator and a communications device used in microwave and milliwave bands and the like.
2. Description of the Related Art
By way of background, an oscillator will be discussed as shown in FIG. 5, it being understood that this oscillator was not publicly known or described in any publication when the present invention was realized and, therefore, is not prior art to the instant invention.
Oscillator 110 comprises a cap 111, a circuit board 140, a dielectric resonator 120, a case 130 and a stem 112. The cap 111 and the stem 112 are made of steel, and terminal pins 113 connect to the stem 112.
The circuit board 140 comprises a circuit pattern, such as a stripline, provided on an insulated substrate. Elements such as a FET 142, a chip capacitor 143 and a chip resistor 144 are mounted at predetermined positions on the circuit board 140, and are connected together. The terminal pins 113 and holes 155a, 155b and 155c, having roughly the same shape as the terminal pins 113, are provided at three corners of the circuit board 140, and terminal electrodes 149, 150 and 153 are provided around the holes 155a, 155b and 155c. The terminal pins 113 are inserted through the holes 155a, 155b and 155c, provided in the circuit board 140, and are connected to the terminal electrodes 149, 150 and 153.
The dielectric resonator 120 comprises a square dielectric substrate 121 and an electrode 122, provided on two opposite faces and four side faces of the dielectric substrate 121. Then, circular electrode removal portions 123 are provided roughly in the center of the electrode 122 on the opposite two faces, opposite to each other. Furthermore, a concave portion 131 for holding the dielectric resonator 120 is provided in the case 130.
The case 130, with the dielectric resonator 120 held therein, is placed on the stem 112, and the circuit board 140 is mounted on the case 130. In this way, the cap 111 is hermetically sealed over the stem 112, on which the case 130 holding the dielectric resonator 120 and the circuit board 140 are mounted.
In an oscillator used at high-frequency bands such as a milliwave band, even a slight discrepancy in the size of the components or their positions etc., will effect the resulting characteristics to a degree which cannot be ignored. For instance, when the positional relationship between the dielectric resonator and the circuit board changes, the coupling between the striplines provided on the circuit board and the dielectric resonator will be altered. This has a considerable effect on the oscillating frequency, the oscillating output, and the like, and as a consequence, the characteristics of the oscillator are unstable. Therefore, in order to manufacture a stable oscillator having desired characteristics, the positional relationship between the dielectric resonator and the circuit board must be adjusted with a precision of below 0.1 mm.
To carry out this adjustment, the dielectric resonator is provided in the concave portion of the case, the circuit board is mounted on the case, and this assembly is covered with the cap. The characteristics of the oscillator are then measured. When the desired characteristics are not obtained, the cap and the circuit board are removed, the position of the dielectric resonator is changed, the circuit board is remounted, the cap is replaced, and the characteristics of the oscillator are measured once more. This operation is repeated until the desired characteristics are obtained.
Thus, in the oscillator shown in FIG. 5, the operation of removing the circuit board and the cap to change the position of the dielectric resonator, and then remounting the circuit board and replacing the cap, must be carried out many times. Consequently, considerable time is needed to obtain an oscillator having the desired characteristics, leading to increased manufacturing costs.